1. Field of the Invention
This invention relates generally to an apparatus for cutting, conveying and stripping segments of wire and more particularly to a programmable wire stripper therefor that will automatically strip preselected variable length insulation portions from the ends of precut wire segments having conductors of the same or differing gauge.
2. Description of Prior Art
In industry there are many applications requiring large numbers of wire segments cut to predetermined lengths with the insulation portion cut, or cut and stripped from the ends thereof and with a suitable end terminal applied. There is a need for batches of individual wire segments all having the same gauge but with the gauge varying from batch to batch and also a need for sets of precut insulated wire segments having conductors of the same or differing gauge with each set to be assembled into a wiring harness. More specifically a precise length of insulation at the end of each wire segment is transversely cut and then stripped from the conductor following which the connector terminals that are required are attached. For some applications the ends of the wire segments may have the insulation cut but not removed in order to protect the ends of multiple wire strand conductors from fraying during shipping.
It is known in the prior art to automatically cut wire segments from several wire spools containing continuous wire coils of differing gauges. The wire segments for a complete harness, for example, are cut in a predetermined sequence, to form one complete harness set and then fed in sequence onto a conveyor mechanism which comprises two laterally spaced apart conveyor units, one of which can be adjusted relative to the other to accommodate wire segments of varying lengths. The conveyor mechanism sequentially carries the cut wire segments to a wire stripping workstation or workstations where the wire stripper cuts the insulation and then strips an insulation slug portion from one or both ends of each wire segment leaving a bare conductor of the desired length.
In the cutting operation, the insulation is cut through transversely of the conductor as completely as possible prior to pulling off the insulation portion using a pair of opposed face-to-face stripping knives which are reciprocated toward and away from the opposite sides of the conductor. Each knife has one or more V-shaped cutting edge profiles (two cutting profiles if two wires are simultaneously stripped) and as the knives are in face-to-face relation their cutting edges coact to define a generally diamond shaped cutting profile which partially surrounds the insulation when the knives are brought together. The conductors are generally circular in cross-section and the stripper knives are set so that when they close they will stop before they actually cut into the wire. This setting, which limits the closing of the knives, is important especially where the conductor comprises a plurality of fine strands of wire. If some of the strands are cut they will be removed with the insulation slug and the rated current carrying capacity of the conductor will be reduced. Further, any cutting or even nicking of the wire will create a weak area which is subject to early fracture when the end of the wire segment is flexed or bent as the wire segment or harness is being installed.
In a stripping operation with V-shaped knives as above described, the insulation sheath is only cut at four points on the periphery of the conductor and indeed may not be quite completely cut through at any point. When the insulation slug portion is removed by pulling it axially off the wire conductor, the insulation is stretched until it tears free at the weakened or cut area. This stretching of insulation frequently results in the insulation which is retained on the wire segment, also stretching to the degree where it will take a set in a stretched out position. This permanent stretching of the insulation is referred to as "milking". When milking occurs, the lengths of the bare stripped portion of the conductor will vary depending on the amount of set that the insulation takes on the wire segment. Uneven lengths of stripped conductors are undesirable because they will cause problems in attaching the ends of terminals which are pre-sized to receive precisely the same lengths of bare conductor in order to permit their automatic attachment to the wire segment.
In an effort to minimize the problem of milking insulation it is known to twist the insulation slug portion before pulling it axially off the wire, but this requires a more complex mechanism. It is also known to grind the cutter knives so that the apex of their V-shaped profile is in the form of a semicircle having a diameter which is slightly greater than the diameter of the conductor so that the insulation will be cleanly cut around its entire periphery while the wire conductor itself will not be nicked or cut. When the apex of the cutter knife is semicircular in profile, the knife is, as a practical matter, only usable for the one specific gauge of wire it was ground to fit. If the degree of closing of the opposed knives is set to accommodate either larger or smaller gauge conductors, the cutter profile of two mating knives no longer forms a true circle and significant amounts of insulation will remain unsevered. When insulation is unsevered, the milking problem will exist or the cut insulation portion will adhere so tightly to the remaining insulation on the wire segments that it will not tear free, but will instead slip out from between the gripping jaws as they withdraw, thus allowing insulation to remain on the end of the wire segment. Insulation portions which remain on the wire segment will disrupt the operation of the terminal applying machine just as uneven lengths of stripped bare conductors will.
From the foregoing it will be understood that a manufacturer of wire segments requires a high speed apparatus to cleanly and quickly strip wires that are in a set having differing gauges of conductors at a single workstation, or to strip the wire segments in batches, with each batch being all of the same gauge but with the wire gauge varying from batch to batch. However, as such wire segments can be cut at an extremely high rate of speed it is undesirable to shut down the stripper in order to change knives or knife settings to accommodate batches of wire segments of differing gauges. An even more difficult problem exists where a plurality of wire segments are being cut to form a set for the purpose of assembly into a wire harness as it is then necessary for the stripper to adjust back and forth between individual wire conductors of differing gauges almost instantly. In addition, it is necessary that the length of the stripped off insulation portion of each wire segment also be variable in order to accommodate different types of end terminals. In theory it is possible to program a single set of knife closings to vary between one of a plurality of closing dimensions which would be keyed to a sequence of different gauges of wire presented at the workstation. However, this type of practice presents at least two problems. First, in order to program the degree of closing of the knives it is necessary to use a cutter ground with a sharp apex notch and therefore the insulation sheath will not be scored or cut completely around its periphery thus causing milking problems when the cut insulation portion is removed. Second, because such equipment is operating at an extremely high rate of speed through millions of cycles it is extremely difficult in practice to constantly maintain the close tolerances for variable position stop means necessary to prevent cutting into the conductor over a long period of time in spite of wear.
Thus, the problem which has not been successfully solved in the prior art is how to provide a stripping apparatus which will present a plurality of wire segments at a workstation where a stripper will be able to strip lengths of insulation from the ends of wire segments, each of which may have a different gauge conductor at an extremely high rate per minute without incurring the problem of milking the insulation or nicking or scraping the conductor while also providing a practical way of varying the length of the stripped portion of insulation from conductor to conductor so as to accommodate various differing styles of wire terminals. It is appreciated by those skilled in the art that if even one end of the plurality of wire segments is not cleanly stripped of insulation to a precise length, the automatic terminal applying machine will be disrupted resulting in the wire segment or entire wiring harness becoming defective. In such event, the entire automated production line is frequently required to be shut down until the problem is corrected. Such shutdowns result in high expense due to labor costs and lost production.